Philosophy, Classification and Phylogeny

From the Greeks to the present day-passing by Darwin-the way in which we classify living beings has remained in constant discussion. Aristotle was one of the first to propose a character based method on a classification system. Theophrastus, Pedanius and Plinius continued to contribute in one way or another to the categorization of life (Manktelow, 2010). In the mid- 18th century, Carl Von Linné introduced the binary classification system, giving a more organized meaning to life, but Linné was only interested in descriptions of the species and was not in organizational levels superior to genres. Lammarck, de Jussieu and Adenson in different ways proposed the use of characters for a hierarchical organization of the species. Lamarck and Juisseu also believed that the similarities of the species corresponded to a continuity in the form. Then emerged the compared anatomy with Cuvier and Leclerc who went deeper into the importance of the characters (Stevens, 2002).

These researchers prior to the theory of natural selection, had in common that they conceived the species as immutable categories, that is, could not emerge new species and these are simply transformed into other “Scala naturae”. With the advent of Darwin and Wallace's theory of natural selection, species began to be understood as groups of organisms that changed their shape by various factors, the idea of the common ancestor gained strength and the change of organisms over time began to be represented with phylogenies (Ruse, 2009), taking the classification from an evolutionary perspective. The use of phylogenies represented in trees made it necessary to establish techniques to infer these trees. So, the definitions of homology and homoplasy became important when choosing the characters, but outside the already famous discussion between the three schools, the philosophical background of the methods used in cladistics has also been generating great controversy from the beginning.

Willi Hennig proposed the maximum parsimony method based on Ockham's knife and Poper's epistemology. Popper believed to have solved the problem of inductivism in science, the problem is about making a posteriori conclusions based on repetitive prior knowledge, since these are merely "historical memories" and have no predictive power-they do not assure what will happen in the future -. For Popper the only important thing is the data at the moment and if a hypothesis can be falsifiable, then it is a valid hypothesis (Reippel, 2003). The falsifiability implies that a theory is capable of being rejected by empirical and verifiable evidence, the rest would be pseudoscience (Popper, 1981). After Hennig, various methods of inference (contrary to popperian ideology) have emerged, that use either likelihood (Maximum Likelihood) or later probability (Bayesian Analysis). These two methods considered deductive by those who defend parsimony -as they use other information besides the data- are considered contradictory to Popper's epistemological theory, however, some authors claim that likelihood can be considered popperian (Helfenbein, 2005).

In my opinion, any type of statement that is made in science must be supported by empirical and explicit evidence, in addition to being subject to falsification, either by new information available or by a new interpretation of the data. It is a good way to avoid falling into dogmatism and to advance in the creation of knowledge.

Bibliography

• Helfenbein, K. G., & DeSalle, R. (2005). Falsifications and corroborations: Karl Popper’s influence on systematics. Molecular Phylogenetics and Evolution, 35(1), 271-280.
• Manktelow, M. (2010). History of taxonomy. Lecture from Dept. of Systematic Biology, Uppsala University.
• Popper, K. (1981). Science, pseudo-science, and falsifiability. Scientific thinking, 92-99.
• Rieppel, O. (2003). Popper and systematics. Systematic Biology, 52(2), 259-271.
• Stevens, P. F. (2003). History of Taxonomy. eLS.
• Ruse, M. (2009). Darwin y la filosofía. teorema, 28(2).